Present evidence suggests that a disturbance in the collapsibility of the upper airway exists in patients with obstructive sleep apnea during sleep and wakefulness. This proposal, by applying concepts of flow through collapsible tubes (Starling resistor), will examine the collapsibility of the human upper airway in both normal individuals and in patients with obstructive sleep apnea. This proposal is based on preliminary observations which have shown that during sleep, normal individuals and patients with obstructive sleep apnea can be distinguished by differences in the collapsibility of the upper airway as refected by changes in the critical pressure (P-crit) of the upper airway. In order to investigate the role of P-crit in health and disease (obstructive sleep apnea), we will vary upstream pressure at the nose to determine critical pressures of the upper airway. Our first specific aim will be to determine the range of critical pressure in normal individuals, normal individuals who snore, and patients with obstructive sleep apnea. Since additional data suggests that abnormal upper airway critical pressures reflect a distrubance in upper airway collapsibility in patients with obstructive sleep apnea, second specific aim will be to determine whether factors that reduce the severity of sleep apnea result in a parallel decrease in P-crit. Specifically, we will investigate the effects of weight loss and protriptyline on upper airway P-crit. Our third specific aim will be to determine whether factors that increase the severity of sleep apnea lead to a parallel rise in critical pressure (P-crit) of the upper airway. Finally, our fourth specific aim will be to relate the effects of uvulopalatopharyngoplasty on the severity of obstructive sleep apnea and P-crit. Specifically, we will explore the relationship between changes in upper airway size following reconstruction of the upper airway and upper airway collapsibility.